Compaction devices are known e.g. in the form of a road roller.
With the aid of a road roller, ground areas, e.g. asphalt surfaces, can be compacted across large surface areas. In order to guarantee the load-bearing capacity and durability of the ground, sufficient compaction is required. In the compaction performed by road rollers, a distinction is made between a dynamic and a static functionality. In case of a dynamic functionality, the compaction is effected by movement, and in case of a static functionality, the compaction is effected by the weight of the road roller.
A road roller can be a self-propelled vehicle and comprises at least one drum.
When negotiating curves with the drum of a compaction device in the form of a road roller, there exist an inner and an outer curve radius of the drum at the lateral ends of the drum. At the outer-curve edge of the drum, due to the longer distance that is being covered there, the speed is higher than at the inner edge. With increased steering angle and a resultant smaller curve radius, the distance between said two speeds will become larger. Since, however, a drum cannot rotate with different peripheral speeds on its lateral ends, the drum will in the middle of its width be rolling on the underlying ground or soil, whereas, on the outer edge regions of the drum, sliding movements (slippage) will occur between the asphalt and the rolling surface of the drum. For this reason, it appears useful to divide the drum and to drive both halves independently from each other so that, due to the smaller width of the divided drum, the above compulsory effect can be reduced.
Oscillation drums, in contrast to vibration drums, are not produced in a divided configuration because the technical realization is distinctly more difficult. The synchronization of the unbalanced masses generating the centrifugal forces must be guaranteed at all times, particularly also in case of a turning of the drums relative to each other.
In a known oscillating roller according to WO 82/01903, two synchronously rotating imbalance shafts are provided which are driven via a central shaft by means of toothed belts. Thereby, a rapidly changing forward/rearward rotating movement is imposed on the roller. As a result, the rotating roller will never be lifted from the underlying ground.
From WO 82/01903 (FIG. 5), there can be gathered four typical operational state of the oscillation system of an undivided oscillation drum of the state of the art. From left to right, the positions of the unbalanced masses are shown as rotated in respective steps of 90° (phase-shifted).
Because of the coupled drive, the two unbalanced masses (imbalance weights) will rotate in the same sense. While, in the operational states in the left-hand views in FIG. 5, the centrifugal forces will eliminate each other, the rotational moment in the views on the right-hand side (FIGS. 5B, 5D), due to the directions of the centrifugal forces F and the lever arms x, will beM=2·x·F in the clockwise (FIG. 5B) and respectively the anticlockwise direction (FIG. 5D).
Thus, with each revolution of the imbalanced shaft, the drum will undergo a slight turn to the left and to the right and will start to oscillate about the rotational axis M of the drum.
In vibration drums, dividing the drum is already known because its technical realization is easy. FIG. 2 of the present description shows a sectional view of a divided vibration drum. The two drum parts 2a,2b are screwed to each other via a rotary connection. Here, the unbalanced masses 3 for both drum parts 2a,2b are arranged on the central imbalanced shaft 31 which is driven by a hydraulic engine 7. When a curve is negotiated and the drum parts 2a,2b are thus turned relative to each other, nothing will change about the vibration of the two drum parts 2a,2b relative to each other, i.e. both drum parts 2a,2b will vibrate in synchronism.
A simple configuration with a continuous central shaft 33 for driving the unbalanced masses 3 as in a vibration drum, is shown in FIG. 3 for an oscillation drum. This approach cannot solve the phase problem for the following reasons:
When the drum parts 2a,2b (roller surfaces) are being turned relative to each other, e.g. while a curve is being negotiated, the position of the unbalanced shafts 31a,31b relative to each other will change because the imbalance shafts 31a,31b are supported in the respective drum parts 2a,2b. Since the unbalanced masses 3, which are driven by toothed belts 32 by a central shaft 33, will maintain their orientation, the direction of the effectiveness of the force in the turned drum part 2a,2b will each time be shifted (FIG. 4 to FIG. 7).
For better representation of the arrangement of the toothed belts of FIG. 4 to FIG. 7, the described arrangement of the toothed belts is shown in perspective view in FIG. 3.
FIG. 4 and FIG. 5 show the two drum parts 2a,2b prior to being turned. In FIG. 6 and FIG. 7, the drum parts 2a,2b are shown after drum part 2b has been turned by 90°.
For explanation, it be assumed that the drum part 2a does not change its position while the drum part 2b continues being turned by 90°. For visualization, also the central rotating shaft is shown in a snapshot and thus is virtually at a standstill. As depicted in FIG. 7, the two unbalanced masses of the right-hand drum part 2b have now been positioned above each other. Since the drive shaft 33 in the center of the drum is at a standstill, the toothed belt 32 during the rotation of drum part 2b has been rolling on the central drive pulley 21 and did not change the orientation of the unbalanced masses 3. However, due to the new positions of the unbalanced masses 3, the centrifugal forces will now initiate, with maximum leverage, a moment which will cause the drum part 2b to rotate. In the position in FIG. 6, on the other hand, no moment is generated since the effective leverage is zero.
The described problematics has the consequence that the drum parts 2a,2b cannot oscillate in synchronism. In the extreme case, when the two drum parts 2a,2b operate exactly contrarily to each other, thrust movements will occur in the gap between the drum parts 2a,2b and in the adjacent regions, so that the asphalt surface will be torn open. Depending on the turning of the drum parts 2a,2b relative to each other, phase errors from 0 to 180° may occur. Already phase errors from 10 to 20° would shear off the asphalt at the joint between the drum parts 2a,2b. 
Thus, it is an object of the invention to provide a vibration device and respectively method for the compacting of ground which is free of the above described problems.